1. Field of the Invention
The present invention relates to a gas separator for use in a fuel cell, and a fuel cell incorporating the gas separator, and a method of production of the gas separator. More particularly, the invention relates to a fuel cell gas separator which is provided between adjacent unit cells in a fuel cell formed by stacking a plurality of unit cells, and which forms a fuel gas passage and an oxidative gas passage, together with adjacent members, and separates a fuel gas and an oxidative gas from each other, and a fuel cell incorporating the gas separator, and a method of production of the gas separator.
2. Description of the Related Art
A fuel cell gas separator is a component member of a fuel cell stack formed by stacking a plurality of unit cells. The gas separator has a sufficiently high gas impermeability so as to prevent mixture of a fuel gas and an oxidative gas that are supplied to adjacent unit cells. A typical fuel cell gas separator is formed by using a carbon material or a metal material. Normally, metal materials have excellent strength, and therefore allow formation of a thinner gas separator than carbon materials. This allows the size of a fuel cell to be reduced. Furthermore, metal-made gas separators can be produced by a simple and easy methods, for example, by pressing a metal sheet, so that the gas separator production process can be simplified and made less time-consuming. Therefore, adoption of a metal-made gas separator improves productivity and controls the production costs.
For production of a metal-made gas separator, a suitable metal may be selected from metals having sufficiently high electric conductivity, strength and formability. Normally, an anticorrosion measure is needed to secure a sufficiently high corrosion resistance of the gas separator under environmental conditions for the operation of a fuel cell. One example of a measure for improving the corrosion resistance of a gas separator is to coat a gas separator with a metal having a good corrosion resistance, for example, platinum, gold, rhodium, iridium and the like (described in, for example, Japanese Patent Application Laid-Open No. HEI 5-182679).
However, these metals are rarely-occurring natural resources, and the use of such a costly noble metal increases the production cost of a fuel cell. Furthermore, if plating or the like method is employed for the metal coating process, the problem of formation of micro-holes in the coating surface is likely to arise. If there are holes in a coating surface, corrosion advances gradually therefrom. Thus, if a gas separator is coated with a noble metal as mentioned above, it is still difficult to secure a sufficiently high corrosion resistance. An attempt may be made to restrict the effect of corrosion starting at holes in a coating surface within an allowable range. However, this attempt necessitates an increase in the coating thickness, thereby increasing the amount of noble metal used. A technology for achieving an improved corrosion resistance of a gas separator by coating it with nickel is known (for example, Japanese Patent Application Laid-Open No. HEI 7-282821). In some cases, however, the nickel coating fails to secure a sufficiently high corrosion resistance under environmental conditions for the operation of a polymer electrolyte fuel cell.